This invention relates to water-based organic coatings and, more particularly, to such coatings which comprise the reaction product of the condensation of water-soluble, low molecular weight esters with a water-soluble aminoplast resin.
Coatings have been required for coating cans which are used, for example, as containers for soda pop and beer and for coating coiled sheet metal before it is subjected to manufacturing operations such as bending, cutting, etc. Such coatings are required to have good flexibility, hardness, durability, decorative appearance, chemical resistance and flow. Among the numerous formulations which have been used to meet these requirements (with varying degrees of success) have been organic solvent-based coatings such as those described in U.S. Pat. No. 3,714,090, issued Jan. 30, 1973, entitled "High Temperature Polyester Coating Composition" and U.S. Pat. No. 3,714,091, issued Jan. 30, 1973, entitled "Oil-Containing Polyester Coating." Although the coatings described in these patents have been highly successful, there is a present need to provide metal coatings with comparable properties which are water soluble as a preferred way of meeting clean air standards.
Water-soluble, ester-based coatings formulations are described in U.S. patent application Ser. No. 246,353, filed Apr. 21, 1972, entitled "Water-based Wood Coatings and Ester Intermediates Thereof." The coatings described therein are particularly useful as wood finishes. Although these latter coatings have many desirable properties which are required for wood coatings, they are generally too brittle and hard for metal applications unless substantially modified.